Defining intermediates and redundancies in coenzyme Q precursor biosynthesis.

Area of Science:

• Biochemistry
• Metabolic Pathways
• Yeast Genetics

Background:

• Coenzyme Q (CoQ) is vital for cellular energy production via oxidative phosphorylation.
• The synthesis of the CoQ head group precursor, 4-hydroxybenzoate (4-HB), from tyrosine in eukaryotes remains largely uncharacterized.
• Specific intermediates and enzymes in the conversion of 4-hydroxyphenylpyruvate (4-HPP) to 4-hydroxybenzaldehyde (4-HBz) were previously undescribed.

Purpose of the Study:

• To elucidate the unknown steps and enzymes in the yeast tyrosine catabolism pathway leading to 4-hydroxybenzoate (4-HB).
• To identify novel intermediates and enzymes involved in Coenzyme Q (CoQ) biosynthesis.
• To understand the redundancy and regulation of this essential metabolic pathway.

Main Methods:

• Utilized genetic screens in Saccharomyces cerevisiae to identify key enzymes.
• Employed targeted liquid chromatography-mass spectrometry (LC-MS) for intermediate identification.
• Applied chemical genetics and isotope labeling studies to trace metabolic flux.

Main Results:

• Identified three redundant aminotransferases (Bna3, Bat2, Aat2) supporting 4-HB production.
• Discovered novel tyrosine catabolites, including 4-hydroxyphenylacetate (4-HPA) and 4-hydroxyphenyllactate (4-HPL).
• Found that 4-hydroxyphenylacetaldehyde (4-HPAA) and 4-hydroxymandelate (4-HMA) can rescue the pathway when supplemented.

Conclusions:

• Defined previously unknown steps in 4-hydroxybenzoate (4-HB) synthesis from tyrosine in yeast.
• Demonstrated significant functional redundancy among aminotransferases in this pathway.
• Provided a foundational understanding for further investigation into CoQ biosynthesis and related metabolic processes.